Among various headphones, a headphone of an over-ear type, for example, is worn on the head of a user who listens to a music sound from a music player or the like. The headphone has a pair of sound emission units and a connection member connecting the sound emission units.
Each sound emission unit includes a driver unit and a housing accommodating the driver unit. The driver unit converts electrical signals (sound signals) from a sound source, such as a music player, into sound waves and outputs the sound waves.
Conventionally, electrical signals to be input into a driver unit of a headphone are analog signals. The driver unit outputs sound waves according to magnitudes of amplitudes and frequencies of analog signals. Thus, when sound signals from a sound source are digital signals, the digital signals are converted into analog signals by a digital-analog converter built in a music player or the like and transmitted to the headphones.
In recent years, a driver unit (hereinafter, referred to as “digital driver unit”) capable of outputting desired sound waves according to digital signals without converting the digital signals into analog signals has been proposed (for example, refer to Japanese Unexamined Patent Publication No. 2012-227589).
The digital driver unit is a driver unit of a dynamic type, and includes one diaphragm and a plurality of voice coils. The individual digital signals (hereinafter, referred to as “processed signals”) are applied to each voice coils. The processed signals are generated by a circuit for signal processing (hereinafter, referred to as “signal processing circuit”). The driver unit disclosed in Japanese Unexamined Patent Publication No. 2012-227589 can reproduce sound signals from a high frequency range to a low frequency range with high efficiency by driving (vibrating) the voice coils in response to processed signals.
By incorporating the digital driver unit and the signal processing circuit in a headphone, a headphone (hereinafter, referred to as “digitally driven headphone”) in which a driving part of the driver unit is driven in response to digital signals is configured.
Among headphones, there is a headphone in which a headphone cable to be connected to a sound source is connected to only one sound emission unit (for example, refer to Japanese Unexamined Patent Publication No. 2010-050647). The headphone disclosed in Japanese Unexamined Patent Publication No. 2010-050647 includes a signal line (hereinafter, referred to as “connecting cord”) transmits sound signals from one sound emission unit to the other sound emission unit. The connecting cord is connected to the inside of one sound emission unit and the inside of the other sound emission unit. The connecting cord is wired inside a connection member.